U.S. patent number 8,912,242 [Application Number 13/347,706] was granted by the patent office on 2014-12-16 for polar polystyrene copolymers for enhanced foaming.
This patent grant is currently assigned to Fina Technology, Inc.. The grantee listed for this patent is Melissa Greenberg, David W. Knoeppel, Wei Wang. Invention is credited to Melissa Greenberg, David W. Knoeppel, Wei Wang.
United States Patent |
8,912,242 |
Wang , et al. |
December 16, 2014 |
Polar polystyrene copolymers for enhanced foaming
Abstract
A method of making a foamable polystyrene composition includes
combining a styrenic monomer and a co-monomer containing a polar
functional group to obtain a mixture, subjecting the mixture to
polymerization to obtain a styrenic co-polymer, and combining the
styrenic co-polymer with a blowing agent in a foaming process to
obtain foamed articles.
Inventors: |
Wang; Wei (League City, TX),
Knoeppel; David W. (League City, TX), Greenberg; Melissa
(Katy, TX) |
Applicant: |
Name |
City |
State |
Country |
Type |
Wang; Wei
Knoeppel; David W.
Greenberg; Melissa |
League City
League City
Katy |
TX
TX
TX |
US
US
US |
|
|
Assignee: |
Fina Technology, Inc. (Houston,
TX)
|
Family
ID: |
46637373 |
Appl.
No.: |
13/347,706 |
Filed: |
January 11, 2012 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120208911 A1 |
Aug 16, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61441389 |
Feb 10, 2011 |
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Current U.S.
Class: |
521/56; 521/146;
521/147 |
Current CPC
Class: |
C08J
9/122 (20130101); C08J 9/142 (20130101); C08J
9/0023 (20130101); C08J 9/12 (20130101); C08F
212/08 (20130101); C08F 212/08 (20130101); C08F
220/281 (20200201); C08F 212/08 (20130101); C08F
222/08 (20130101); C08F 212/08 (20130101); C08F
220/1804 (20200201); C08F 212/08 (20130101); C08F
220/325 (20200201); C08J 2203/12 (20130101); C08J
2351/00 (20130101); C08J 2325/08 (20130101); C08J
2203/10 (20130101); C08J 2203/06 (20130101) |
Current International
Class: |
C08J
9/06 (20060101); C08J 9/10 (20060101) |
Field of
Search: |
;521/56,146,147 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Zemel; Irina S
Claims
What is claimed is:
1. A foamable polystyrene composition comprising: a blowing agent
comprising carbon dioxide (CO.sub.2); and a styrenic co-polymer
resulting from polymerization of a reaction mixture comprising a
styrenic monomer and from 0.5 to 20 wt % a co-monomer comprising a
polar functional that is hydroxyethylmethacrylate (HEMA) or
caprolactone acrylate, wherein the styrenic co-polymer exhibits
increased solubility of CO.sub.2 and decreased diffusivity of
CO.sub.2 in comparison to a styrene polymer that is not modified
with a co-monomer having a polar functional group.
2. The foamable polystyrene composition of claim 1, wherein the
styrenic monomer is selected from the group consisting of styrene,
alpha-methyl styrene, vinyl toluene, p-methyl styrene, t-butyl
styrene, o-chlorostyrene, vinyl pyridine, and any combinations
thereof.
3. The foamable polystyrene composition of claim 1, wherein the
co-monomer comprising a polar functional group is present in
amounts ranging from 0.5 to 10 wt % based on the total weight of
the reaction mixture.
4. The foamable polystyrene composition of claim 1, wherein the
co-monomer comprising a polar functional group is caprolactone
acrylate.
5. The foamable polystyrene composition of claim 1, wherein styrene
is present in amounts ranging from 90 to 99 wt % based on the total
weight of the styrenic co-polymer.
6. The foamable polystyrene composition of claim 1, wherein the
co-monomer comprising a polar functional group is HEMA.
7. The foamable polystyrene composition of claim 1, wherein the
blowing agent is entirely composed of the CO.sub.2.
8. The foamable polystyrene composition of claim 1, wherein the
blowing agent further comprises water (H.sub.2O), ethanol, air,
nitrogen, argon, helium or combinations thereof.
9. The foamable polystyrene composition of claim 1, wherein the
blowing agent is present in the styrenic co-polymer in a weight
proportion ranging from 1 to 30 parts per 100 parts of styrenic
material.
10. A polystyrene foam obtained from the foamable polystyrene
composition of claim 1.
11. An article made from the polystyrene foam of claim 10.
12. A method of making a polar polystyrene copolymer comprising:
combining a styrene monomer and a polar co-monomer that is
hydroxyethylmethacrylate (HEMA) or caprolactone acrylate to obtain
a reaction mixture, wherein the reaction mixture comprises from 0.5
to 20 wt % of the polar co-monomer; subjecting the reaction mixture
to polymerization conditions to obtain a styrenic co-polymer; and
combining the styrenic co-polymer with a blowing agent comprising
carbon dioxide (CO.sub.2) to obtain a foamable blend, wherein the
styrenic co-polymer exhibits increased solubility of CO.sub.2 and
decreased diffusivity of CO.sub.2 in comparison to a styrene
polymer that is not modified with a co-monomer having a polar
functional group.
13. The method of claim 12, wherein the polar co-monomer is
caprolactone acrylate.
14. The method of claim 12, wherein the polar co-monomer is
HEMA.
15. The method of claim 12, wherein the polar co-monomer is added
to the reaction mixture in amounts ranging from 0.5 to 10 wt %
based on the total weight of the reaction mixture.
16. The method of claim 12, wherein the blowing agent further
comprises water (H.sub.2O), ethanol, air, nitrogen, argon, helium
or combinations thereof.
17. The method of claim 12, wherein the blowing agent is added to
the styrenic co-polymer in a weight proportion ranging from 1 to 30
parts per 100 parts of styrenic co-polymer.
18. An expandable polystyrene, comprising: a styrenic copolymer;
and a blowing agent comprising carbon dioxide (CO.sub.2); wherein
the styrenic polymer results from polymerization of a reaction
mixture of a styrene monomer and from 1 to 20 wt % of a co-monomer
having a polar functional group, wherein the styrenic copolymer
exhibits increased solubility of CO.sub.2 and decreased diffusivity
of CO.sub.2 in comparison to a styrene polymer that is not modified
with a co-monomer having a polar functional group; wherein the
co-monomer having a polar functional group is
hydroxyethylmethacrylate (HEMA) or caprolactone acrylate.
19. The expandable polystyrene of claim 18, wherein the co-monomer
having a polar functional group is caprolactone acrylate.
20. The expandable polystyrene of claim 18, wherein the blowing
agent further comprises water (H.sub.2O), ethanol, air, nitrogen,
argon, helium or combinations thereof.
21. The expandable polystyrene of claim 18, wherein the blowing
agent is incorporated into the expandable polystyrene in a weight
proportion ranging from 1 to 30 parts per 100 parts of the styrenic
copolymer.
22. The foamable polystyrene composition of claim 18, wherein the
co-monomer comprising a polar functional group is HEMA.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a non-provisional of U.S. Provisional
Application Ser. No. 61/441,389 filed Feb. 10, 2011.
FIELD
The present invention is generally related to polymeric
compositions. More specifically, the present invention is related
to foamable polystyrene compositions.
BACKGROUND
Styrene, also known, as vinyl benzene, is an aromatic compound that
is produced in industrial quantities from ethylbenzene. The most
common method of styrene production comprises the dehydrogenation
of ethylbenzene, which produces a crude product of styrene monomer
and unreacted ethylbenzene and hydrogen. Polystyrene is an aromatic
polymer produced from the styrene monomer. Polystyrene is a widely
used polymer found in insulation, packaging, and disposable
cutlery.
Different types of polystyrene materials can include
general-purpose polystyrene (GPPS), high impact polystyrene (HIPS),
and transparent impact polystyrene (TIPS). Many conditions affect
the properties of the resulting product, including processing time,
temperature, pressure, purity of the monomer feedstock, and the
presence of additives or other compounds. These and other
processing conditions alter the physical and chemical properties of
the polystyrene product, affecting the suitability for a desired
use.
Foamed polystyrene offers the advantages of low cost and high
structural strength for its density. A typical polystyrene foam
also has a relatively high impact resistance and possesses
excellent electrical and thermal insulation characteristics. Foamed
polystyrene is useful in a variety of applications such as
insulation, packaging, coolers, food packaging, decorative pieces,
and dunnage. Additionally, polystyrene foams are commonly
classified into three general categories: low density, medium
density, and high density. Low density polystyrene foams usually
have a density of from about 1 to about 3 lb/ft.sup.3 whereas
medium density foams may have a density ranging from about 4 to
about 19 lb/ft.sup.3 and high density foams often have a density
ranging from 20 to about 30 lb/ft.sup.3.
The two main types of polystyrene foam are extruded polystyrene
(XPS) foam and expanded polystyrene (EPS) foam. Extruded
polystyrene foam is typically formed by mixing polystyrene with
additives and blowing agents into an extruder that heats the
mixture. The mixture is then extruded, foamed to the desired shape,
and cooled. Expanded polystyrene foam is typically formed by
expanding solid polystyrene beads containing a blowing agent such
as pentane with steam or hot gas. These pre-expanded beads may
later be molded into the desired shape and expanded again with
steam or hot gas to fuse the beads together.
In the production of foamed polystyrene, it is common to utilize
blowing agents such as methyl chloride, ethyl chloride,
chlorocarbons, fluorocarbons (including HFCs) and
chlorofluorocarbons (CFCs). However, such blowing agents have been
heavily regulated due to potential environmental impact. Many of
these traditional and current physical blowing agents are
halogenated compounds, which demonstrate a high solubility in polar
polymers. An ongoing trend in foaming process development is to
find environmentally benign chemicals as blowing agents. Some
foaming processes have been using carbon dioxide (CO.sub.2) as the
blowing agent or co-blowing agent. The advantages of using CO.sub.2
include low cost, minimal environmental impact, and eliminating
potential fire hazards. It has therefore been desirable to use
carbon dioxide as a blowing agent from both environmental and
economic standpoints.
However, carbon dioxide has presented problems when used as a
blowing agent. Carbon dioxide has been found to have a relatively
low solubility in styrenic polymer melts. For example, the
solubility of CO.sub.2 in polystyrene is only ca. 4 wt % at 6.5 MPa
and 373 K, as measured by Yoshiyuki Sato et. al. (Journal of
Supercritical Fluids 2001, 19, 187-198.). The low solubility
results in high extrusion pressures, which increases costs and
reduces quality. The low solubility also results in a higher
density product. It would be desirable to obtain a polystyrene
product having a high carbon dioxide solubility in order to reduce
costs and increase product quality.
Furthermore, carbon dioxide has relatively higher vapor pressure
and diffusivity, compared to halogenated blowing agents. In the
extrusion foaming process using CO2 as the blowing agent, the melt
strength of polystyrene is often inadequate, which leads to
immature bubble breakage/coalescence, non-uniform cell morphology,
and excessive open cell content. It would be desirable to obtain a
polystyrene resin having improved melt strength in order to perform
well in foaming processes.
SUMMARY
An embodiment of the present invention is a polystyrene product
that is a styrenic co-polymer resulting from polymerization of a
reaction mixture of a styrenic monomer and co-monomers having polar
functional groups. The polystyrene can then be used in an extrusion
foaming process with the presence of blowing agents.
In a non-limiting embodiment, either by itself or in combination
with any other aspect of the invention, the styrenic monomer can be
selected from the group consisting of styrene, alpha-methyl
styrene, vinyl toluene, p-methyl styrene, t-butyl styrene,
o-chlorostyrene, vinyl pyridine, and any combinations thereof, and
can be present in amounts ranging from 80 to 99.9 wt % based on the
total weight of the expandable polystyrene.
In a non-limiting embodiment, either by itself or in combination
with any other aspect of the invention, the co-monomer can be
selected from the group consisting of hydroxyethylmethacrylate
(HEMA), caprolactone acrylate, alkyl (meth)acrylate, fluorinated
(meth)acrylate and any other polymerizable monomers containing
esters, ethers, carboxylic acids or silanes, and combinations
thereof, and can be present in amounts ranging from 0.5 to 20 wt %
based on the total weight of the reaction mixture.
In a non-limiting embodiment, either by itself or in combination
with any other aspect of the invention, the blowing agent can be
carbon dioxide (CO.sub.2), water (H.sub.2O), ethanol, air,
nitrogen, argon, and helium and combinations thereof and can be
present in the styrenic co-polymer in a weight proportion ranging
from 1 to 30 parts per 100 parts of styrenic material.
In a non-limiting embodiment, either by itself or in combination
with any other aspect of the invention, the present invention
includes any article made from the polystyrene of any embodiment
disclosed herein.
Other possible embodiments include two or more of the above aspects
of the invention. In an embodiment the method includes all of the
above aspects and the various procedures can be carried out in any
order.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph illustrating polylactic acid (PLA) particle size
distribution from PLA blends with various polystyrene
copolymers.
FIG. 2 is a graph illustrating PLA particle size distribution from
PLA blends modified with styrene-maleic anhydride (SMA).
FIG. 3 is a graph of results from haul-off melt strength tests at
various HEMA concentrations.
FIG. 4 is a diagram illustrating the experimental scheme of dynamic
gravimetric measurement of CO.sub.2 solubility.
FIG. 5 is a graph of CO.sub.2 desorption versus CO.sub.2
solubility.
FIG. 6 is a graph of CO.sub.2 desorption versus normalized CO.sub.2
solubility.
DETAILED DESCRIPTION
The present invention includes styrenic polymers and polymer
blends. In an embodiment, the present invention includes styrenic
copolymers of styrene and a second monomer containing a polar
functional group. In a more specific embodiment, the present
invention includes a foamable polymeric composition containing such
styrenic copolymers.
In an embodiment, the present invention includes a styrenic
polymer. In another embodiment, the styrenic polymer includes
polymers of monovinylaromatic compounds, such as styrene,
alpamethyl styrene and ring-substituted styrenes. In an alternative
embodiment, the styrenic polymer includes a homopolymer and/or
copolymer of polystyrene. Styrenic monomers for use in the styrenic
polymer composition can be selected from the group of styrene,
alpha-methyl styrene, vinyl toluene, t-butyl styrene,
o-chlorostyrene, vinyl pyridine, and any combinations thereof. The
styrenic polymeric component in the blend of the present invention
can be produced by any known process.
The styrenic polymer of the present invention may include
general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS),
styrenic copolymer compositions, or any combinations thereof. In an
embodiment, the HIPS contains an elastomeric material. In an
embodiment, the HIPS contains an elastomeric phase embedded in the
polystyrene matrix, which results in the polystyrene having an
increased impact resistance.
The blend of the present invention may contain any desired amounts
of a styrenic polymer. In an embodiment, the blend contains at
least 50 wt % of a styrenic polymer. In another embodiment, the
blend contains a styrenic polymer in amounts ranging from 1 to 99
wt %, 50 to 95 wt %, 60 to 92 wt %, and optionally 70 to 90 wt %.
In a further embodiment, the blend contains a styrene polymer in
amounts ranging from 80 to 99 wt %. In an even further embodiment,
the blend contains a styrenic polymer in amounts ranging from 90 to
95 wt %.
The styrenic polymer of the present invention may be formed by
co-polymerizing a first monomer with a second monomer. The first
monomer and the second monomer may be co-polymerized by having the
first monomer and the second monomer present in a reaction mixture
that is subjected to polymerization conditions. The first monomer
may include monovinylaromatic compounds, such as styrene,
alpha-methyl styrene and ring-substituted styrenes. In an
embodiment, the first monomer is selected from the group of
styrene, alpha-methyl styrene, vinyl toluene, t-butyl styrene,
o-chlorostyrene, vinyl pyridine, and any combinations thereof. In
another embodiment, styrene is used exclusively as the first
monomer. In an embodiment, the first monomer is present in the
reaction mixture in amounts of at least 50 wt % of the reaction
mixture. In another embodiment, the first monomer is present in the
reaction mixture in amounts ranging from 80 to 99.9 wt % of the
reaction mixture. In a further embodiment, the first monomer is
present in the reaction mixture in amounts ranging from 90 to 99 wt
%. Embodiments of the second monomer can be any suitable monomer
capable of polymerization to form a styrenic copolymer. Examples of
suitable second monomers can include hydroxyethylmethacrylate,
caprolactone acrylate, alkyl (meth)acrylate, fluorinated
(meth)acrylate and any other polymerizable monomers containing
polar functionalities such as esters, ethers, carboxylic acids or
silanes, and combinations thereof.
Embodiments of the present invention include at least one second
monomer containing a polar functional group. The second monomer
containing a polar functional group may also be referred to herein
as a "polar monomer". In an embodiment, the polar monomer is a
polar vinyl functional monomer. In another embodiment, the polar
monomer is selected from the group of hydroxyethylmethacrylate,
caprolactone acrylate, alkyl (meth)acrylate, fluorinated
(meth)acrylate and any other polymerizable monomers containing
polar functionalities such as esters, ethers, carboxylic acids or
silanes, and combinations thereof. In a further embodiment, the
polar monomer is selected from the group of caprolactone acrylate,
polyvinyl acetate, and HEMA, and combinations thereof. In an even
further embodiment, the polar monomer is HEMA. In another
embodiment the second monomer may be selected from the group of,
maleic anhydride (MAH), butyl acrylate, butyl methacrylate, and
combinations thereof.
The styrenic polymer of the present invention may be prepared by
polymerizing a reaction mixture containing a first monomer and a
second monomer having a polar functional group. The first monomer
and second monomer may be present in the reaction mixture in any
desired amounts. In an embodiment, the second monomer is present in
the reaction mixture in amounts of at least 0.1 wt % of the
reaction mixture. In another embodiment, the second monomer is
present in the reaction mixture in amounts of less than 20 wt % of
the reaction mixture. In an alternative embodiment, the second
monomer is present in the reaction mixture in amounts ranging from
1 to 20 wt %. In a further embodiment, the second monomer is
present in the reaction mixture in amounts ranging from 1 to 10 wt
%. In an even further embodiment, the second monomer is present in
the reaction mixture in amounts ranging from 1 to 5 wt %.
The polymerization of the styrenic monomer and the polar co-monomer
may be carried out using any method known to one having ordinary
skill in the art or performing such polymerizations. In an
embodiment, the polymerization may be carried out by using a
polymerization initiator. In an embodiment, the polymerization
initiators include but are not limited to perketals,
hydroperoxides, peroxycarbonates and the like. In another
embodiment, the polymerization initiators may be selected from the
group of benzoyl peroxide, lauroyl peroxide, t-butyl
peroxybenzoate, and
1,1-di-t-butylperoxy-2,4-di-t-butylcycleohexane, and combinations
thereof. In an embodiment, the amount of the polymerization
initiator is from 0.01 to 1.0 wt % of the reaction mixture. In
another embodiment, the amount of the polymerization initiator is
from 0.01 to 0.5 wt % of the reaction mixture. In a further
embodiment, the amount of the polymerization initiator is from
0.025 to 0.05 wt % of the reaction mixture.
Any process capable of processing or polymerizing styrenic monomers
may be used to prepare the styrenic co-polymer of the present
invention. In an embodiment, the polymerization reaction to prepare
the styrenic co-polymer may be carried out in a solution or mass
polymerization process. Mass polymerization, or bulk
polymerization, refers to the polymerization of a monomer in the
absence of any medium other than the monomers and a catalyst or
polymerization initiator. Solution polymerization refers to a
polymerization process in wherein the monomers and polymerization
initiators are dissolved in a non-monomeric liquid solvent at the
beginning of the polymerization reaction.
The polymerization may be either a batch process or a continuous
process. In an embodiment, the polymerization reaction may be
carried out using a continuous production process in a
polymerization apparatus including a single reactor or multiple
reactors. The styrenic polymer composition can be prepared using an
upflow reactor, a downflow reactor, or any combinations thereof.
The reactors and conditions for the production of a polymer
composition, specifically polystyrene, are disclosed in U.S. Pat.
No. 4,777,210, which is incorporated by reference herein in its
entirety.
The temperature ranges useful in the polymerization process of the
present disclosure can be selected to be consistent with the
operational characteristics of the equipment used to perform the
polymerization. In an embodiment, the polymerization temperature
ranges from 90 to 240.degree. C. In another embodiment, the
polymerization temperature ranges from 100 to 180.degree. C. In yet
another embodiment, the polymerization reaction may be carried out
in multiple reactors in which each reactor is operated under an
optimum temperature range. For example, the polymerization reaction
may be carried out in a reactor system employing a first
polymerization reactor and a second polymerization reactor that may
be either continuously stirred tank reactors (CSTR) or plug-flow
reactors. In an embodiment, a polymerization process for the
production of a styrenic co-polymer of the type disclosed herein
containing multiple reactors may have the first reactor (e.g., a
CSTR), also referred to as a prepolymerization reactor, operated
under temperatures ranging from 90 to 135.degree. C. while the
second reactor (e.g. CSTR or plug flow) may be operated under
temperatures ranging from 100 to 165.degree. C.
In an alternative embodiment, the co-polymer may be obtained by
polymerization in which heat is used as the initiator. In a further
embodiment, the co-polymer may be prepared using a non-conventional
initiator such as a metallocene catalyst as is disclosed in U.S.
Pat. No. 6,706,827 to Lyu, et al., which is incorporated herein by
reference in its entirety. In one embodiment, the monomers may be
admixed with a solvent and then polymerized. In another embodiment,
one of the monomers is dissolved in the other and then polymerized.
In still another embodiment, the monomers may be fed concurrently
and separately to a reactor, either neat or dissolved in a solvent,
such as mineral oil. In yet another embodiment, the second monomer
may be prepared in-situ or immediately prior to the polymerization
by admixing the raw material components, such as an unsaturated
acid or anhydride and a metal alkoxide, in-line or in the reactor.
Any process for polymerizing monomers having polymerizable
unsaturation know to be useful to those of ordinary skill in the
art in preparing such polymers may be used. For example, the
process disclosed in U.S. Pat. No. 5,540,813 to Sosa, et al., may
be used and is incorporated herein by reference in its entirety.
The processes disclosed in U.S. Pat. No. 3,660,535 to Finch, et
al., and U.S. Pat. No. 3,658,946 to Bronstert, et al., may be used
and are both incorporated herein by reference in their entirety.
Any process for preparing general purpose polystyrene may be used
to prepare the styrenic co-polymer of the present invention.
In certain embodiments, the styrenic copolymer may be admixed with
additives prior to being used in end use applications. For example,
the styrenic copolymer may be admixed with additives that include
without limitation, antioxidants, UV stabilizers or absorbents,
lubricants, plasticizers, ultra-violet screening agents, oxidants,
anti-static agents, fire retardants, processing oils, mold release
agents, fillers, pigments/dyes, coloring agents, and other similar
compositions. Any additive known to those of ordinary skill in the
art to be useful in the preparation of styrenic copolymers may be
used. CO.sub.2 solubility may increase for lower molecular weight
polystyrene copolymer, therefore, it would be desirable to maintain
or control the molecular weight of the styrenic copolymer. In an
embodiment, chain transfer agents and/or diluents may be added
before and/or during polymerization in order to help control the
molecular weight of the resulting styrenic copolymer.
The obtained polystyrene copolymer may then be sent to an extruder
or other step to obtain an end use article. The blowing agents such
as HFC or CO.sub.2 can be added into the polymer during the
extrusion process.
In an embodiment, styrene monomer is combined with a polar
comonomer and a plasticizer and subsequently polymerized to form a
polar polystyrene copolymer. The polar polystyrene copolymer can
then be sent to an extruder or other step to obtain an end use
article. The blowing agents are added to the polystyrene containing
composition during the extruding step.
In an embodiment, styrene monomer is combined with a second polar
monomer and subsequently polymerized to form a polystyrene
copolymer. In an embodiment, the polystyrene copolymer is sent to
an extruder or other step to obtain an end use article. The blowing
agents are added to the polystyrene containing composition during
the extruding step.
The present invention may include foamed articles which may be
formed by melting and mixing the styrenic copolymer of the
invention to form a polymer melt, incorporating a blowing agent
into the polymer melt to form a foamable blend, and extruding the
foamable blend through a die to form the foamed structure. During
melting and mixing, the polymeric material may be heated to a
temperature at or above the glass transition temperature of the
polymeric material. The melting and mixing of polymeric material
and any additives may be accomplished by any means known in the
art, including extruding, mixing, and/or blending. In an
embodiment, a blowing agent is blended with molten polymeric
material. The blending of the blowing agent with the molten
polymeric material may be performed under atmospheric or elevated
pressures.
In an embodiment, the blowing agent is incorporated into the
styrenic copolymer in a weight proportion ranging from 1 to 30
parts per 100 parts of the polymeric material to be foamed. In
another embodiment, the blowing agent is incorporated into the
styrenic copolymer in a weight proportion ranging from 2 to 18 per
100 parts per polymeric material to be foamed. In a further
embodiment, the blowing agent is incorporated into the styrenic
copolymer in a weight proportion ranging from 4 to 12 parts per 100
parts per polymeric material to be foamed.
The blowing agents of the present invention may include organic
and/or inorganic compounds. In an embodiment, the blowing agents of
the present invention are environmentally benign than methyl
chloride, ethyl chloride, chlorocarbons, fluorocarbons (including
HFCs) and chlorofluorocarbons (CFCs). In a further embodiment, the
blowing agents of the present invention are selected from the group
of carbon dioxide (CO.sub.2), water (H.sub.2O), ethanol, air,
nitrogen, argon, butane, pentane, and helium and combinations
thereof. In an even further embodiment, the blowing agent of the
present invention is entirely composed of CO.sub.2.
The foamable blend may be cooled after the blowing agent is
incorporated into the styrenic blend. In an embodiment, the
foamable blend is cooled to temperatures ranging from 30 to
150.degree. C., optionally 75 to 150.degree. C. The cooled foamable
blend may then be passed through a die into a zone of lower
pressure to form an article of foamed structure. The polystyrene
copolymer can be used for not only foams, but also rigid
blends.
The obtained foamed polystyrene copolymer may have any desired
density. In an embodiment, the density of the foamed polystyrene
copolymer ranges from 15 to 0.1 lbs/ft.sup.3. In another
embodiment, the density of the foamed polystyrene copolymer ranges
from 10 to 0.5 lbs/ft.sup.3. In a further embodiment, the density
of the foamed polystyrene copolymer ranges from 3 to 0.6
lbs/ft.sup.3.
An end use article may include a polystyrene copolymer of the
present invention. In an embodiment, the articles include films and
thermoformed or foamed articles. For example, a final article may
be thermoformed from a sheet containing the polystyrene copolymer.
In another embodiment, the end use articles include foamed
articles, which may have a foamed structure. In an embodiment, an
article can be obtained by subjecting the polymeric composition to
a plastics shaping process such as extrusion. The polymeric
composition may be formed into end use articles including food
packaging, food/beverage containers, polymeric foam substrate,
foamed insulation, building insulation, protective head gear, toys,
dunnage, and the like.
In an embodiment, the obtained polystyrene foam is a multicellular
article having a plurality of cells that may be open or closed. In
another embodiment, the majority of the cells are open. In an
alternative embodiment, the majority of the cells are closed.
EXAMPLES
Example 1
A series of polystyrene samples were made with the addition of
polar modifiers as listed in Table 1 below. The polymerization
reaction was carried out in a CSTR-type batch reactor. Lupersol-233
was added as the initiator with an initial concentration of about
170 ppm in the reaction mixture. The reaction was then run
isothermally at 130.degree. C. with continuous agitation at 150 rpm
for about 3 hours or until 75% conversion was obtained. The
reaction mixture was then transferred onto an aluminum surface and
devolatized under active vacuum of less than 10 torr at 225.degree.
C. for 45 minutes.
The polar modifiers listed in Table 1 include styrene-maleic
anhydride (SMA), a copolymer of styrene and maleic anhydride, which
are commercially available from Sartomer Company, Inc. SMA.RTM.
1000P, SMA.RTM. 3000P and SMA.RTM. EF80 have styrene-to-maleic
anhydride molar ratios of 1:1, 3:1 and 8:1, respectively. The polar
modifiers also include butyl acrylate, butyl methacrylate,
hydroxyethylmethacrylate (HEMA), and maleic anhydride (MAH). The
loading of modifiers is 5 wt %, except for maleic anhydride (MAH).
The loading of MAH is limited to 3.5 wt % and, in a separate
sample, 1.75 wt % due to its limited solubility in styrene. In
Table 1, below, PDI represents polydispersity index wherein
PDI=Mw/Mn, Tg.sub.1 represents the first glass transition
temperature and Tg.sub.2 represents a second glass transition
temperature, if applicable.
TABLE-US-00001 TABLE 1 Characterization of Modified Polystyrene SMA
1000P Modifier None (1:1) SMA 3000P (3:1) SMA EF80 (8:1) wt % 0 5.0
5.0 5.0 mol(# of moles of 0 0.025 0.012 0.005 polar monomer
unit)/(100 g of polymer) Transparency Clear Opaque Opaque Opaque
Tg.sub.1 105.2 104.8 104.5 104.4 Tg.sub.2 n/a 169.3 n/a n/a Melt
Flow Rate 2.1 2.2 2.8 2.9 Mn 130,000 138,000 132,000 84,100 Mw
271,000 273,000 269,000 262,000 Mz 415,000 439,000 418,000 417,000
PDI 2.1 2.0 2.0 3.1 Peak MW 259,000 255,000 259,000 265,000 Butyl
Butyl Modifier Acrylate Methacrylate HEMA MAH MAH wt % 5.0 5.0 5.0
1.75 3.5 mol(# of moles of 0.039 0.035 0.038 0.018 0.036 polar
monomer unit)/(100 g of polymer) Transparency Clear Clear Clear
Clear Semi-clear Tg.sub.1 94.8 98.2 102.6 105.0 104.0 Tg.sub.2 n/a
n/a n/a n/a n/a Melt Flow Rate 3.3 2.9 1.7 2.2 3.3 Mn 136,000
122,000 128,000 115,000 97,300 Mw 184,000 260,000 312,000 250,000
220,000 Mz 433,000 398,000 529,000 391,000 350,000 PDI 2.1 2.1 2.4
2.2 2.3 Peak MW 271,000 250,000 270,000 239,000 212,000
An indicator of polarity change in polystyrene is how well the
material blends with another polar polymer such as polylactic acid
(PLA). In this experiment, the modified polystyrene samples above
were blended with 5 wt. % PLA 3251D (NatureWorks.RTM. Ingeo.TM.) in
a Haake mixer. The Haake mixer was operated at a temperature of
210.degree. C. under a nitrogen atmosphere for 3 minutes with
agitation speeds of 60 rpm. The size of the PLA particles in the
blends were evaluated by solution dynamic light scattering. The
blend samples were dispersed in methyl ethyl ketone (MEK), a good
solvent for polystyrene but not for PLA. FIG. 1 and FIG. 2 show the
PLA particle size distribution from different polystyrene blends.
FIG. 1 compares polystyrene copolymerized with different
comonomers. All of the polystyrene copolymer samples show improved
dispersion of PLA when compared to crystal polystyrene, which
suggests the polarity change in PS and better polar interaction
with PLA. Use of HEMA in PS gave the best result with a relatively
narrower distribution peaked at particle sizes of 0.5 .mu.m.
Similar but slightly worse results were obtained with polystyrene
modified by butyl-acrylate/methacryates as well as maleic
anhydride.
FIG. 2 compares polystyrene modified with different styrene-maleic
anhydride copolymers (SMAs). The SMAs were incorporated into
polystyrene during batch reactions. The PLA particle size
distributions from the SMA blends did not seem to improve much
compared to unmodified PS. The SMAs were not as effective as polar
comonomers, probably due to the relatively lower molar
concentration of polar groups of SMAs under the same weight
percentage loading (see Table 1 above). In addition, the SMAs
containing the higher percentage of maleic anhydride (such as 1000P
and 3000P) are less soluble in styrene. A miscible blend of GPPS
and SMA was only made with SMA EF80, which has a styrene-to-maleic
anhydride of 8:1 and contains the lowest concentration of maleic
anhydride among the various SMAs used. FIG. 2 also shows that use
of HEMA comonomer achieved the best result with a relatively
narrower particle size distribution peaked at particle sizes of 0.5
.mu.m.
Example 2
Hydroxyl functional polystyrene was prepared in a batch reaction
process by copolymerizing styrene with 2-hydroxyethyl methacrylate
(HEMA) at varied concentrations ranging from 0 to 5 wt. % in the
feed (see Table 2). The polymerization reaction was carried out in
a CSTR-type batch reactor. Lupersol-233 was added as the initiator
with an initial concentration of about 170 ppm in the reaction
mixture. The reaction was then run isothermally at 130.degree. C.
with continuous agitation at 150 rpm for about 3 hours or until 75%
conversion was obtained. The reaction mixture was then transferred
onto an aluminum surface and devolatized under active vacuum of
less than 10 torr at 225.degree. C. for 45 minutes.
TABLE-US-00002 TABLE 2 Feed Formulations in Batch Synthesis of
HEMA-modified polystyrene Run No. 1 2 3 4 Styrene (grams) 200 198
195 190 HEMA (grams) 0 2 5 10 HEMA (wt. %) 0 1.0 2.5 5.0 TOTAL
(grams) 200 200 200 200
The concentration effect of hydroxyl groups on polystyrene
properties is shown in Table 3 below. It appears that the measured
molecular weights (Mw and Mz) increase while the melt flow rate
decreases as the concentration of HEMA increases. The results
suggest strengthened inter-chain interactions among polystyrene
chains, possible due to the presence of polar interactions such as
hydrogen bonding. The haul-off melt strength tests were also
conducted on the polystyrene samples. A clear trend can be observed
in FIG. 3, i.e., the melt strength of the material increases along
with the concentration of HEMA. The improvement in the melt
strength is desirable for foaming of polystyrene using CO.sub.2 as
the blowing agent.
TABLE-US-00003 TABLE 3 Characterization of HEMA-modified
polystyrene Mn Mw Mz PDI MFI HEMA (g (g (g Mp Mw/ (g 10 Tg (wt. %)
mol.sup.-1) mol.sup.-1) mol.sup.-1) (g mol.sup.-1) Mn min.sup.-1)
(.degree. C.) 0.0 129,000 269,000 408,000 260,000 2.1 2.2 104.4 1.0
135,000 329,000 515,000 309,000 2.4 1.1~2.5 104.1 2.5 142,000
336,000 523,000 315,000 2.4 1.9~2.3 103.2 5.0 127,000 355,000
584,000 320,000 2.8 0.3 103.1
Example 3
Polymerization reactions were conducted to prepare PS copolymers
containing different polar functional co-monomers. As described in
earlier examples, the polymerization reaction was carried out in a
CSTR-type batch reactor. Lupersol-233 was added as the initiator
with an initial concentration of about 170 ppm in the reaction
mixture. The reaction was then run isothermally at 130.degree. C.
with continuous agitation at 150 rpm for about 3 hours or until 75%
conversion was obtained. The reaction mixture was then transferred
onto an aluminum surface and devolatized under active vacuum of
less than 10 torr at 225.degree. C. for 45 minutes.
The co-monomers used include 2-hydroxylethyl methacrylate (HEMA,
98%, CAS#868-77-9), glycidyl methacrylate (GMA, CAS#106-91-2),
butyl methacrylate (Butyl MA, CAS#97-88-1), isodecyl methacrylate
(Isodecyl MA, CAS#29964-84-9), 2,2,3,4,4,4-hexafluorobutyl acrylate
(Fluorinated, CAS#54052-90-3), 3-(trimethoxysilyl)propyl
methacrylate (Silyl, CAS#2530-85-0), caprolactone acrylate
(Caprolactone, CAS#110489-05-9), methoxy polyethylene glycol (350)
monomethacrylate (PEG350-MA, CAS#26915-72-0) or methoxy
polyethylene glycol (550) monomethacrylate (PEG550-MA,
CAS#26915-72-0).
The solubility and diffusivity of CO.sub.2 in the copolymers were
subsequently measured using the method described below. The results
are listed in Table 4, with other characterization data.
Example 4
Measurement of CO.sub.2 Solubility
The general scheme of measurement is illustrated in FIG. 4. Polymer
samples were molded into disks with a thickness of 1.4 mm and a
diameter of 25 mm. The relatively large surface area on both sides
of the disks ensures that the diffusion of gas occurs mainly in the
normal direction of the disk planes. The sample disk was weighed
(M.sub.ini) and then transferred into a Parr pressure vessel, which
was purged with CO.sub.2 at least 3 times, subsequently heated to
50.degree. C. and pressurized with carbon dioxide to 1,500 psi to
reach a supercritical state. Both temperature and pressure were
maintained for a period of time (t.sub.3 in FIG. 4) to allow
CO.sub.2 absorption into the sample disk. The pressure is then
released instantaneously to atmosphere (at t.sub.4). The sample
disk is quickly taken from the pressure vessel and placed onto a
moisture balance (Ohaus) to record the weight loss as a function of
time under ambient conditions. Reduction of sample weight was
observed due to desorption of CO.sub.2. The dynamic evolution of
weight (M.sub.t) was recorded by a computer and WinWedge program.
The dynamic weight change of the sample disk recorded (after
t.sub.5) was used to calculate the CO.sub.2 solubility as well as
diffusivity with the aid of Fick's diffusion law and appropriate
boundary conditions. The weight data recorded (after t.sub.5) can
be extrapolated to the initial weight (at t.sub.4), prior to the
depressurization, to obtain the CO.sub.2 absorption concentration
as well as the desorption rate of CO.sub.2.
The amount of CO.sub.2 remaining in the sample disk at any given
moment can be represented by M.sub.gas,t and calculated according
to equation: M.sub.gas,t=(M.sub.t-M.sub.ini)/M.sub.iniX100%. The
amount of CO.sub.2 dissolved in a sample under equilibrium
conditions is M.sub.gas,t at t=0, i.e., right before the
depressurization. M.sub.gas,t should drop as a function of time (t)
and eventually approach zero when t=.infin..
To find the amount of CO.sub.2 dissolved in the sample prior to the
depressurization, one needs to extrapolate the data to t=0.
Assuming a constant diffusion coefficient of CO.sub.2, it can be
shown from literature that M.sub.gas,t is a linear function of the
square root of time:
.pi..times..times. ##EQU00001## where l is the thickness of the
sample disk and D is the diffusion coefficient of CO.sub.2. Use of
this equation implicitly assumes uniformity of the initial gas
concentration and homogeneity and isotropy of the sample structure.
It also implies that the diffusion coefficient is constant
regardless of the desorption time, gas concentration in the sample
during desorption and temperature variation which could exist
during the depressurization process. By making a linear plot of
M.sub.gas,t vs. t.sub.1/2, one can calculate M.sub.gas,0 and D from
the intercept (at t=0) and slope, which corresponds to CO.sub.2
solubility and diffusivity in the sample polymer, respectively.
CO.sub.2 Solubility in Modified PS
Dynamic CO.sub.2 solubility measurements were conducted on an
un-modified PS reference, commercial poly(styrene-co-acrylonitrile)
(SAN) and a series of polarity-modified PS lab samples. Table 4
below lists the results by the name of co-monomers in the
polystyrene copolymers. A plot of CO.sub.2 diffusivity versus
solubility of various samples was also constructed as shown in FIG.
5.
Compared to the un-modified polystyrene, SAN showed significantly
higher CO.sub.2 solubility (15.6%) and lower CO.sub.2 desorption
diffusivity (1.1.times.10.sup.-7 cm.sup.2/s). The affinity of polar
groups in SAN toward CO.sub.2 may partially explain, from an
enthalpy point of view, the enhanced (thermodynamic) solubility and
slowed (kinetic) diffusivity. The swelling in CO.sub.2 was small
(<5% in thickness) for both SAN and PS.
Besides SAN, it is clear that all the polarity-modified PS
copolymers show higher CO.sub.2 solubility, more or less, when
compared to the un-modified PS reference. The greatest CO.sub.2
solubility enhancement was observed on 3-(trimethoxysilyl)propyl
methacrylate-modified PS (Silyl-PS) with a 20% increase of
solubility. This was followed by PS copolymerized with alkyl
methacrylates or fluorinated acrylate. The fact that none of the
samples has lower CO.sub.2 solubility than the un-modified PS
demonstrates the effectiveness of polarity-driven structural
modification of PS for CO.sub.2 solubility enhancement.
The high gas diffusivity is not desired for foaming processes as it
has a negative impact on cell morphology control and can lead to
accelerated gas exchange with air (foam aging). Among the different
modified PS tested, there appear to be a few copolymers which
actually show lower diffusivity than the un-modified PS reference.
Examples include HEMA-, alkyl methacrylate- and
caprolactone-modified PS.
TABLE-US-00004 TABLE 4 CO.sub.2 Solubility and Diffusivity in PS
Copolymers (CO2 Soaking Conditions: 1500 psi, 50.degree. C.)
Solubility Diffusivity Co-monomer (g per 100 g (10.sup.-7
cm.sup.2sec.sup.-1, MI Sample (wt. %) polymer) 25.degree. C.) Swell
% T.sub.g (.degree. C.) (g/10 min) Mn Mw Mz Mw/Mn Mp PS Ref. 0 10.1
2.8 5% 104 2.2 129,000 269,000 308,000 2.1 260,000 SAN 25 15.6 1.1
4% 105 165000* HEMA 5.0 10.7 1.9 3% 103 0.3 127,000 355,000 584,000
2.8 320,000 HEMA 2.5 11.0 2.6 7% 103 1.9 142,000 336,000 523,000
2.4 315,000 GMA 5.0 11.0 3.0 4% 101 2.4 125,000 277,000 435,000 2.2
261,000 Butyl MA 5.0 11.4 2.3 2% 98 2.9 122,000 260,000 398,000 2.1
250,000 Isodecyl MA 5.0 11.7 2.8 13% 94 3.0 141,000 362,000 668,000
2.6 273,000 Flurinated 5.0 11.7 3.0 12% 96 n/a 125,000 265,000
409,000 2.1 252,000 Silyl 2.5 10.2 3.5 6% 101 2.6 128,000 298,000
493,000 2.3 260,000 Silyl 5.0 12.1 5.8 36% 97 n/a 132,000 335,000
630,000 2.5 261,000 Caprolactone 2.5 10.8 2.2 9% 92 n/a 139,000
522,000 1,144,000 3.8 248,000 PEG350 MA 5.0 11.4 n/a n/a 81 0.3
69,000 383,000 1,107,000 5.6 167,000 PEG550 MA 5.0 11.0 5.0 30% 80
4.4 106,000 334,000 681,000 3.2 242,000
The measured CO.sub.2 solubility data have indicated enhanced
CO.sub.2 solubility when the polar co-monomers of various
concentrations are incorporated into polystyrene. To compare the
modifier efficiency in CO.sub.2 solubility improvement, the portion
of CO.sub.2 solubility contributed by the co-monomer was normalized
based on the weight. The normalized data (Table 5 and FIG. 6)
showed that the silyl methacrylate and HEMA were more effective to
boost CO.sub.2 solubility than other co-monomers. Interestingly,
acrylonitrile had only moderate efficiency on CO.sub.2 solubility
enhancement, comparable to isodecyl- and fluorinated acrylates.
TABLE-US-00005 TABLE 5 Normalized CO.sub.2 Solubility and
Diffusivity in PS Copolymers (CO2 Soaking Conditions: 1500 psi,
50.degree. C.) Solubility Diffusivity Co- (g per 100 g Solubility
Contribution- S.sub.CO2-extra/Mass (10.sup.-7 cm.sup.2sec.sup.-1,
Sample monomer(wt. %) polymer) Comonomer (S.sub.CO2-extra) of
Comonomer 25.degree. C.) PS Ref. 0 10.1 0.0 0.10 2.8 SAN 25 15.6
8.0 3.32 1.1 HEMA 5.0 10.7 1.1 0.22 1.9 HEMA 2.5 11.0 1.2 0.46 2.6
GMA 5.0 11.0 1.4 0.28 3.0 Butyl MA 5.0 11.4 1.8 0.36 2.3 Isodecyl
MA 5.0 11.7 2.1 0.42 2.8 Flurinated 5.0 11.7 2.1 0.42 3.0 Silyl 2.5
10.2 0.4 0.14 3.5 Silyl 5.0 12.1 2.5 0.50 5.8 Caprolactone 2.5 10.8
1.0 0.38 2.2 PEG350 MA 5.0 11.4 1.8 0.36 n/a PEG550 MA 5.0 11.0 1.4
0.28 5.0
With both diffusivity and normalized solubility considered, there
appeared to be a few co-monomers which achieved a good balance of
diffusivity and solubility. Examples included the caprolactone,
butyl and hydroxyethyl methacrylate modified PS. The CO.sub.2
solubility improvement in these modified PS exceeded that in SAN
while the diffusivity was well contained to be below that in the
un-modified PS. Commercial SAN has a very low CO.sub.2 diffusivity
of 1.1.times.10.sup.-7 cm.sup.2/s, despite its high CO.sub.2
solubility.
Overall, the results clearly demonstrate that the presence of polar
groups in polystyrene can lead to a higher CO.sub.2 solubility. A
CO.sub.2 solubility enhancement will benefit foaming of polystyrene
using CO2 as the blowing agent.
As used herein, the term "monomer" refers to a relatively simple
compound, usually containing carbon and of low molecular weight,
which can react by combining one or more similar compounds with
itself to produce a polymer.
As used herein, the term "co-monomer" refers to a monomer that is
copolymerized with at least one different monomer in a
copolymerization reaction resulting in a copolymer.
As used herein, the term "homopolymer" refers to a polymer
resulting from polymerization of a single monomer species.
As used herein, the term "co-polymer," also known as a
"heteropolymer," is a polymer resulting from polymerization of two
or more monomer species.
As used herein, the term "copolymerization" refers to the
simultaneous polymerization of two or more monomer species.
As used herein, the term "polymer" generally includes, but is not
limited to homopolymers, co-polymers, such as, for example, block,
graft, random and alternating copolymers, and combinations and
modifications thereof.
As used herein, the terms "Continuous Stirred Tank Reactor,"
"Continuously Stirred Tank Reactor" and "CSTR," refer to a tank
which has a rotor that stirs reagents within the tank to ensure
proper mixing, a CSTR can be used for a variety of reactions and
processes and is generally known in the art.
The various embodiments of the present invention can be joined in
combination with other embodiments of the invention and the listed
embodiments herein are not meant to limit the invention. All
combinations of various embodiments of the invention are enabled,
even if not given in a particular example herein.
While illustrative embodiments have been depicted and described,
modifications thereof can be made by one skilled in the art without
departing from the spirit and scope of the disclosure. Where
numerical ranges or limitations are expressly stated, such express
ranges or limitations should be understood to include iterative
ranges or limitations of like magnitude falling within the
expressly stated ranges or limitations (e.g., from about 1 to about
10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12,
0.13, etc.).
Use of the term "optionally" with respect to any element of a claim
is intended to mean that the subject element is required, or
alternatively, is not required. Both alternatives are intended to
be within the scope of the claim. Use of broader terms such as
comprises, includes, having, etc. should be understood to provide
support for narrower terms such as consisting of, consisting
essentially of, comprised substantially of, etc.
Depending on the context, all references herein to the "invention"
may in some cases refer to certain specific embodiments only. In
other cases it may refer to subject matter recited in one or more,
but not necessarily all, of the claims. While the foregoing is
directed to embodiments, versions and examples of the present
invention, which are included to enable a person of ordinary skill
in the art to make and use the inventions when the information in
this patent is combined with available information and technology,
the inventions are not limited to only these particular
embodiments, versions and examples. Also, it is within the scope of
this disclosure that the aspects and embodiments disclosed herein
are usable and combinable with every other embodiment and/or aspect
disclosed herein, and consequently, this disclosure is enabling for
any and all combinations of the embodiments and/or aspects
disclosed herein. Other and further embodiments, versions and
examples of the invention may be devised without departing from the
basic scope thereof and the scope thereof is determined by the
claims that follow.
* * * * *